1. Field of the Invention
The present invention relates to organic waste treatment and, more particularly, to a system for converting organic waste reservoirs into anaerobic digesters.
2. Description of the Prior Art
Throughout the world where there is large hog livestock, the management of the hog manure is problematic. The hog manure is often stored and subsequently spread on fields as a fertilizer. However, raw manure is quite toxic and detrimental to the environment by polluting the air, the water and the soil. In order to overcome this problem, the raw hog manure must be treated. Accordingly, various treatment methods have been developed. One of these methods consists in promoting the action of certain types of bacteria contained in the hog manure so that these bacteria digest the organic matter in transforming the latter into an inert and deodorized fertilizer. The basic conditions of this digestion process are the absence of air and the obtention of an appropriate constant temperature. This process is characterized as anaerobic digestion and is at the root of the present invention.
The raw hog manure is typically stored within cylindrical concrete reservoirs. When such reservoirs are not covered, the precipitation, e.g. rain, are allowed to fall into the reservoirs, thereby increasing the volume of the manure and, thus, the cost associated with the transportation thereof. Furthermore, the presence of oxygen promotes the proliferation of a particular type of bacteria that produce carbonic gas (CO2), which is associated with nauseating odors. Open reservoirs also permit the evaporation of the nitrogen contained in the raw manure, which significantly reduces the fertilizing potential thereof.
Reservoirs containing other types of organic waste also suffers from similar drawbacks. Accordingly, there is a need for a new system which could be adapted to a variety of organic waste reservoirs to convert the same into anaerobic digesters.
It is therefore an aim of the present invention to provide a new system for converting a reservoir into an anaerobic digester.
It is also an aim of the present invention to provide a new roof structure which is adapted to seal a reservoir from the atmosphere.
It is a further aim of the present invention to provide a new sealing system which is adapted to be installed on a reservoir to seal it from the atmosphere while allowing the recovery of the biogas generated during the anaerobic transformation of the organic waste contained in the reservoir.
Therefore, in accordance with the present invention, there is provided a system for converting a reservoir into an anaerobic digester in which organic waste contained in the reservoir can be at least partly anaerobically decomposed. The system comprises a roof structure adapted to be installed on the reservoir to seal the reservoir from the atmosphere. The roof structure includes a gas-impermeable membrane adapted to extend over the organic waste contained in the reservoir for trapping, beneath the gas-impermeable membrane, gas generated during decomposition of the organic waste in the reservoir. The gas-impermeable membrane has a peripheral depending skirt adapted to extend downwardly and inwardly of an inner surface of a surrounding containing wall of the reservoir below a level of organic waste to prevent the gas from escaping along the inner surface of the reservoir.
In accordance with a further general aspect of the present invention, there is provided an anaerobic digester comprising a surrounding wall forming a digester vessel for containing an organic waste material, and a roof structure for sealing the digester vessel from the atmosphere. The roof structure comprises a gas-impermeable membrane adapted to extend over the organic waste contained in said digester vessel for trapping, beneath said gas-impermeable membrane, gas generated from a decomposition of the organic waste. The gas-impermeable membrane has a peripheral depending skirt adapted to extend downwardly and inwardly of an inner surface of the surrounding wall of the digester vessel below a level of organic waste to prevent the gas from escaping along the inner surface.
In accordance with a further general aspect of the present invention, there is provided a system for converting an existing reservoir containing an organic waste into an anaerobic digester, comprising an inflatable roof structure adapted to be installed on the existing reservoir for allowing anaerobic conditions to be reached therein, and a gas removal unit for removing gas captured beneath said inflatable roof structure from the existing reservoir.
In accordance with a still further general aspect of the present invention, there is provided a system for converting a reservoir containing organic waste into an anaerobic digester, comprising a roof structure adapted to be installed on the reservoir to seal the same from the atmosphere, wherein said roof structure includes a gas-impermeable membrane adapted to float on top of the organic waste to raise and lower with a level of the organic waste while at the same time trapping gas generated from the decomposition of the organic waste beneath said gas-impermeable membrane.